Phenytoin quinone is a metabolite of phenytoin. Phenytoin sodium is a commonly used antiepileptic. Phenytoin acts to suppress the abnormal brain activity seen in seizure by reducing electrical conductance among brain cells by stabilizing the inactive state of voltage-gated sodium channels. Aside from seizures, it is an option in the treatment of trigeminal neuralgia in the event that carbamazepine or other first-line treatment seems inappropriate. It is sometimes considered a class 1b antiarrhythmic. (Wikipedia)